MESS: Modified Exponential Subjective Scoring Implemented

Following the August 2020 chain reorganization attacks, Ethereum Classic implemented ECBP-1100 — Modified Exponential Subjective Scoring (MESS) — a novel approach to enhancing chain security without introducing centralized checkpoints.

## What is MESS?

MESS adds a "gravity" penalty to chain reorganizations, making it exponentially more difficult to replace recent blocks. It works by requiring increasingly more total work to displace the current chain tip as the reorganization depth grows.

## How It Works

MESS assigns a gravity score to chain tips based on:
- The length of the chain segment being replaced
- How recently the blocks were produced
- Total accumulated difficulty

Longer reorganizations require proportionally more work to succeed, making deep reorgs economically prohibitive without changing the fundamental proof-of-work consensus mechanism.

## Benefits

- **Attack Resistance**: Made 51% attacks significantly more expensive — an attacker needs not just majority hashrate but exponentially more work for deeper reorgs
- **No Centralization**: Does not rely on checkpoints, trusted parties, or finality gadgets
- **Preserves PoW Model**: Transactions still achieve probabilistic finality through proof-of-work

## Deprecation

MESS was deprecated after Ethereum's Merge in September 2022, when GPU miners migrated to ETC and network hashrate increased from ~25 TH/s to over 200 TH/s. At that hashrate level, the economic cost of a 51% attack became prohibitively expensive without MESS, and the additional reorganization penalty was no longer necessary.

## Specification

ECBP-1100 is documented in the Ethereum Classic Improvement Proposals repository.